Pulleys have been in use for centuries to reverse a pulling force, but their designs have not kept pace with the availability of new materials or methods of manufacture. Currently available pulleys cannot be used effectively when the pulling rope, cable, chain, knots, splices, connector joints, or foreign matter such as accumulated aquatic weeds or other vegetation become tangled with the pulley. Entanglements are caused either by the pulley not pointing midway between the pulling force and the object being pulled, or by what is being pulled through the pulley being larger than the space provided within the pulley.
Currently available pulleys are designed for specific rope or chain sizes that allow minimum space for knots or obstructions to pass through the pulley; the pulling rope or chain may tangle with the frame when tension is not continuously maintained; and the excessive weight of heavy duty pulleys makes their use impractical in many aquatic applications.